The following news release issued today by the University of Queensland, Australia, describes research that overturns a long-held theory in plant science. Researchers at the U.S. Department of Energy's Brookhaven National Laboratory who are co-authors on this paper conducted critical radiotracer studies that support the new theory that plant sugars play a dominant role in regulating branching at plant stems. While branching has relevance in agriculture, it is also very important in bioenergy crop production. For more information about Brookhaven's role, see the sidebar, or contact Karen McNulty Walsh, (631) 344-8350, kmcnulty@bnl.gov.

Sugar Responsible for Shoot Branching in Plants

April 8, 2014

Tracking Sugar Movement in Plants

Brookhaven plant biologist Benjamin Babst and Brittany Wienclaw, who was a summer intern as part of the DOE SULI program at Brookhaven while working on her undergraduate degree at the University of New Haven, conducted an essential experiment to verify that sugars play a key role in apical dominance and the regulation of plant bud growth. The aim of their part of this study was to test if sugars produced in leaves via photosynthesis move downward through plants in greater quantities when shoot tips are removed, and quickly enough to trigger bud growth farther down.

To trace the sugars, the scientists first had to add a radioactive "tag" to these molecules... MORE

A University of Queensland study has overturned the long-held belief that plant hormones control the shape of plant growth.

Instead, it has shown that this process starts with sugar.

Shoot branching in plants is a vital process in agriculture and this finding will contribute toward the Queensland Government's goal to double agricultural production by 2040 and the global need to increase food production.

The study's senior author, Professor Christine Beveridge from UQ's School of Biological Sciences, said the finding would help increase crop productivity by improving plant structure.

"The growth of shoots and number of branches are very important to productivity and profitability, particularly in crops such as avocado, macadamia and mango," she said.

"We discovered that this process is initiated by sugar rather than hormones, as previously believed.

"This discovery is so simple yet it has been overlooked for nearly a century."

Previous studies have focused on the plant hormone auxin as the regulator of shoot branching.

5-hour time-lapse film of experimental plants under various conditions. (A) In intact plants, the shoot tip inhibits the growth of the axillary buds below. (B) Decapitation results in a release of apical dominance and induces rapid bud growth. Scientists had thought this was due to depletion of the plant signaling hormone auxin, but blocking stem transport with a girdle (C) results in auxin depletion with no induction of bud growth. (D) Girdling prior to decapitation prevents rapid bud release, because the girdle inhibits the movement of sugars, now known to be the primary factor for triggering bud growth immediately following decapitation.

Professor Beveridge and her team showed that shoot branching can begin up to 24 hours before auxin levels change, so it cannot be responsible for initiating this process.

Instead they found that shoot growth occurs when a high concentration of simple sugar (table sugar) produced by the plant through photosynthesis - is available.

"Plants have a 'Goliath' main shoot, which hoards the sugars to promote its growth," Professor Beveridge said.

"If the main shoot is damaged or removed the sugars are quickly redistributed to start the growth of new shoots.

"As gardeners know, deliberately removing the main shoot will direct a plant's growth outward rather than upward, which can be very important in agriculture."

UQ is working with The Queensland Alliance for Agriculture and Food Innovation (QAAFI), Horticulture Australia Limited (HAL), NSW Department of Primary Industries and the Queensland Department of Agriculture, Fisheries and Forestry (DAFF) to transform the productivity and profitability of tropical and subtropical tree crops.

Dr John Wilkie, principal horticulturalist and head of this initiative at DAFF, said the discovery would further research into how tree crops divide sugar between tree growth and fruiting.

"Manipulating the number of branches can optimise the production of fruit and seeds, leading to greater agricultural productivity," he said.

The research was published in the Proceedings of the National Academy of Sciences on 7 April 2014.

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